1. Field of the Invention
The present invention relates to a charged particle beam processing apparatus for drawing a pattern such as an LSI on a substrate by an electron beam and for applying processing to a surface of the substrate by a convergent ion beam.
2. Description of the Related Art
In recent years, there has been a further growing demand for improvement of the integrity and precision of an LSI. There has been very stringent the specification of a line width and dimensional precision of a pattern to be drawn on a substrate such as a mask (or reticule) for use in manufacture of the LSI.
Therefore, an expensive mask drawing apparatus having its highly advanced performance is required to manufacture a highly advanced mask. Further, a mask drawing time is increased due to the improvement of the integrity and downsizing, and thus, a mask manufacturing cost is increasing higher. In addition, a number of steps including a mask drawing step followed by a developing step, an etching step, an inspection step, a correction step and the like are required for manufacturing the mask. Considering the costs of these steps, it is predicted that the mask manufacturing cost becomes huge.
Therefore, an utmost effort for improving the yield of mask manufacturing is made in order to reduce an increase of the mask manufacturing cost to its required minimum.
The largest factor of lowering the yield of mask manufacturing is a defect of a pattern of a manufactured mask, and the largest cause of this defect is a particle (foreign object) on a mask substrate such as dust, damage, or dirt.
In particular, in the case where a particle exists on a mask substrate before drawn, and if the particle is present in an exposure region, a portion at which the particle has existed surely remains as a defect. The defect is detected in the inspection step that follows the drawing step, the developing step, and the etching step, and the correction or discarding process is carried out. Therefore, the key to improvement of the yield is how to surely detect a particle which causes a defect before drawing and discard the mask substrate having the particle.
Thus, each manufacture makes an utmost effort for how to prevent a particle such as dust from adhering to mask blanks before drawn (hereinafter, referred to as a “substrate”).
When drawing a pattern on a substrate, it is necessary to set the substrate in a drawing apparatus and to transport the substrate into a sample chamber. However, at this stage, there is a very high possibility of dust or dirt newly adhering onto the substrate. In particular, there exist a variety of opportunities of adhering of a particle such as adhering of dust which occurs at the time of a shock or vibration on the way of transporting the substrate or at the time of transporting the substrate from an atmospheric environment to a vacuum environment.
Among them, the most important is that it is unavoidable that the substrate and a structure on a stage in the sample chamber come into contact with each other when the substrate is installed on the stage. In addition, it is general to press the substrate against a positional reference (an object to be pressed) on the stage to thereby determine a drawing position of the substrate on the stage. However, at this time as well, a positioning mechanism comes into contact with the substrate, whereby there is a high possibility that a dust occurs.
Therefore, in recent years, there has been proposed a method for merely placing the substrate on a substrate holding unit on the stage without pressing the substrate against the positional reference when the substrate is installed on the stage in the sample chamber. In this case, no positioning is carried out on the stage, and thus, there is a danger that a position of the substrate on the stage and a position of a pattern to be drawn are shifted from each other.
If a position shift of the drawing pattern on the substrate occurs, a large amount of time is required for pre-alignment of detecting a position of a pattern formed on the substrate by means of a stepper using the substrate or the like, or detection may be impossible.
Thus, in order to detect the position of the substrate on the stage, there has been thought a method for detecting the position and a rotation angle of the substrate, correcting a drawing pattern, and correcting a setup position of the substrate by an image processing technique using a CCD camera or the like (Jpn. Pat. Appln. KOKAI Publication No. 2002-280287).
However, in the case of using the image processing technique using the CCD camera or the like, there is a problem that there is a high possibility of incorrect recognition for the different optical characteristics of substrate surfaces. The different optical characteristics is cased by a surface condition of substrate under detection object. The surface condition of substrate is determined by for example a method for applying resist or, a formed state of a light shielding film such as a Cr film. The different optical characteristics is further cased by type of the substrate (for example, a Levenson mask or a half tone mask or like).
In addition, when an attempt is made to precisely detect the position of the substrate, a CCD camera must be installed near an electron optical mirror cylinder of the sample chamber, so that there is a danger that drawing precision is adversely affected by an electromagnetic wave (noise) which leaks from the CCD camera.
Moreover, in order to detect a position of a substrate by carrying out image processing using the CCD camera or the like, there is a need for complicated processing operations such as detecting an image of a specific mark and capturing an image of the vicinity of an side face of the substrate in order to calibrate a positional relationship with a CCD image on the stage; carrying out pattern recognition from an image of an side face or the like; and detecting a position and a rotation angle of the side face.
Further, there is a need for additional illumination means for illuminating the substrate in a vacuum sample chamber in order to obtain an optical image, and a drawing apparatus itself and a detecting process become complicated.
As described above, in the prior art, when the substrate is installed on the stage in the sample chamber of the charged particle beam drawing apparatus, there is a possibility that a position shift of a drawing pattern on the substrate occurs if the setup position of the substrate is shifted. When the positional reference (the object to be pressed) or the like is used in order to prevent the shifting, there is a danger that particles generate. In addition, when using the image processing technique using the CCD camera or the like, a noise which impairs the drawing precision is generated or the CCD camera, its optical system and illumination system make the apparatus complicated. Moreover, there is a problem that a variety of works such as image and coordinate calibration are required.